Radiotelephone equipment



E G. e. BRADLEY 2,458,558

RADIO TELEPHONE EQUIPMENT Jan. 11, 1949.

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Filed July 26, 1946 To ENVENTOR 13, 655: f 5AOLEX Jan. 11, 1949. g.BRADLEY 2,458,558-

RADIO TELEPHONE EQUIPMENT Filed July 26, 1946 2 Sheets-Shae 2 law) 64(o/V7201. flan-E Pan 5e In;

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Hy lNVENTOR meqe lie/amen ATTORN EY Patented Jan. 11, 1949 2,458,558RADIOTELEPHONE EQUIPMENT George G. Bradley, Great Neck, N. Y., assignorto Radio Corporation of America, a corporation of Delaware ApplicationJuly 26, 1946, Serial No. 686,265

17 Claims.

This invention relates to-radio-telephone equipment.

It has particular application in two-way radiotelephone service where itis required to operate between ships and on ship-to-shore service. Theinvention is well adapted to the communication needs of ships which plyour inland water ways, such as rivers and lakes.

My invention is exemplified in certain radiotelephone equipment whichhas been built and successfully tested and which, as a specificembodiment, comprises transmitting circuits pretuned to as many as sixradio frequency channels and six radio receivers, also pre-tuned.

The main body of the equipment, including the radio circuits, is usuallylocated at some point remote from the operators station. It is thereforerequired that it be completely operated by remote control. Preferably onship-board two telephone stations are installed, one, say, in the pilothouse, and the other in the radio operators cabin or captains quarters.The different transmitting circuits and receivers are adjusted forservice on assigned carrier waves, such as have been provided by theFederal Communications Commission for use on the Mississippi River andits tributaries, or on the Great Lakes. The frequency range is withinthe limits of 2000 to 9000 kilocycles. The power output of thetransmitter is preferably in the 75 watt range. The equipment has beenproven satisfactory for service over distances as great as 800 miles. Inpla and answering calls a frequency channel is usually chosen among sixthat are available whereby optimum conditions of communication may bechosen according to the time of day and with respect to the distancebetween stations.

Among the many noteworthy objects of my invention are the following,which are considered the more important:

1. To provide a flexibly operable two-way radio communication systemespecially adapted for use between ships and on ship-to-shore service oninland waterways, such as rivers and lakes.

2. To provide radio-telephone equipment the transmitter of which isserviceable with a minimum of delay for answering a call, and which willgive satisfactory service over distances up to 800 miles.

3. To provide equipment for radio-telephone communication selectively onany one of a plurality of I frequency channels certain of which wouldbeallocated in the 4, 6 and/or 8 megacycle bands for daytime service,other channels being preferably allocated in the 2 to 3 megacycle bandfor general service over land and fresh water; for example, betweenvessels which navigate the Mississippi River and its tributaries.

4. To provide radio-telephone equipment for use on ship-board wherebythe placing of outgoing calls and the answering of incoming calls may beexpeditiously handled at either of two stations, the main part of theinstallation being remotely situated.

5. To provide for continuous monitoring of incoming calls by means of aplurality of receivers, say six, which are operable in a stand-bycondition; each receiver being tuned to a difierent frequency channeland their outputs being impressed upon aloud speaker or a selective.rcall responsive device which responds to specific code signals andcauses an alarm to be sounded upon reception of its code number.

6. To provide specialized switching devices in a multi-channelradio-telephone system whereby during a telephone conversation over aselected radio frequency channel all receivers are momentarily silencedWhile talking; all receivers of unused channels are completely silenceduntil the conversation is ended; and whereby the unused one of twotelephone stations is rendered incapable of operation to in any wayinterfere with or intercept a communication carried on from the stationmomentarily in use.

My invention will now be described in more detail, reference being madeto the accompanying drawings in which a single circuit diagram is shownby Figs. 1 and 2. Fig. 215 to be placed on the right'hand side of Fig.1, so that the conductors which appear to run from one figure to theother maybe placed in registry.

Referring first to Fig. 1, this figure in its entirety represents acontrol unit A for one telephone station. This control unit comprises ahook switch IOI whereon a hand-set I02 may be hung when not in use. Thecontrol unit also includes a loud speaker I03 which is principally usedfor continuous monitoring of incoming calls on the three medium or lowfrequency channels. A bell I04 is also provided in the control unit. Aswill be explained hereinafter, this bell is sounded by relay operationwhenever a selective ringer I05 responds to code signals. This selectiveringer is preferably connected through a ringer amplifier I06 to theoutput terminals of three receivers D, E and F which are tuned to thehigher frequencies.

A channel selector switch having a multiplicity of ganged contact wipersand cooperating contacts' wafers, lettered a to 1 inclusive, is providedfor use of the equipment on any of six radio frequency channels,numbered I to 6 inclusive. The gang switch also has a position forstand-by operation, so that continuous monitoring of incoming calls maybe had on any of the six receivers ,three of which would impress theircalls upon the loud speaker and the other three of which would beresponsive by way of soundingthe alarm through the selective ringer Iand bell I04.

The control unit A shown in Fig. 1 may be the sole telephone station onboard, but preferably two such units are provided. In Fig. 2, thereforeI have shown as a block diagramv asecond control unit B the componentsof which will be understood to be exact duplicates of what is providedin control unit A.

The radio equipment is housed in a single cabinet which may be locatedwherever spacev can be conveniently found on shipboard. This cabinetcontains the radio circuits of the transmit,- ters and receivers, alsocertain switching devices which are remotely controlled from the controlstations. Furthermore it houses the selective ringer I05. and amotor-generator for the transmitter power supply. The motor-generator isnot shown, but it will be understood that it requires starting mechanismfor which a control circuit 209 is provided. The receivers are operatedfrom the ships D. C. power line. The motor-generator is operated onlywhen carrying on a conversation and provides anode, screen and negativebiasing voltages for the transmitter tubes.

In order to provide for exclusive control of, the, equipment from eitherone of the two control units A and B, I provide certain relay equipmentin a junction box. This relay equipment in combination with theswitchingdevices of the control units is described and claimed in aco-pending application filed by myself jointly with Harry F; Mohr Ser.No. 679,344 on June. 26, 1946'. Other than terminals, the junction boxcontains only the relays 60I, 602 and 604, the first two relaysbeingparallel-connected.

The control unit The remote control unit with which the handset I02 isassociated is provided with a switch I01 having connections 8| and 82to-a similar switch at control unit B. Either of these switches may beused to connect or disconnect the ships 115.-volt D. C. power line +L toor from the telephone equipment. A pilot lamp I08 lights upwhen theships line is connected to. the receivers. Switch I09A or I093 is usedfor selecting the particular control unit- A or- B respectively w-hereata callis to be placed or answered. Assuming that thehand-set at controlunit B has not been lifted switch I09A operates (before lifting'the handset)v to. transfer telephone service from control unit. B to controlunit A. Switch I I0 is; provided for choosing between loud speaker and,earphone receoption. The hand-set, I02 is provided with. a push-button II I- which must be depressed when talking. In the hand-set is agroundconnection common to the terminals of the earphone, the microphone andthe push-button. The pushbutton circuit may be traced from groundthrough conductor 30, contacts of relay 60-2, the coil. of relay- I12and thenceto the negative terminal-C of the transmitter power supply, inwhich the +C' is ground potential.

Thev relay II'2 operates two movable contacts b, and e. which. areassociated with front contactsa, and cl respectively, and contact enormally rests.

4 against back contact 1. Several functions ar performed as folows: (1)Closure of contacts at and e supplies negative line potential (-L) tothe winding of relay II4 on the other side of which +L potential issupplied through normally closed contacts b and c of relay I I3. Relay II4 operates, therefore, as a slave to relay I I2. (2) The breaking ofcontacts e and f on relay II2 opens the cathode and gain controlcircuits of all the receivers, thus silencing the same. (3) Closure ofcontacts a. and b on relay I I2 in series with contacts f and g on relayII4 removes a blocking potential from the cathodes of the oscillator andthe power amplifier tubes for keying the transmitter carrier on. This isaccomplished by effectively short-circuiting resistor I22 (4700 ohms)through the very low value resistor I57 (5 ohms). Normally (with thepush-button not depressed) the carrier wave is not propagated because ofa positive potential applied to the cathodes just mentioned. Thispositive potential results from the voltage drop (approximately volts)-through resistor I22 which carries a bleedercurrent derived from avoltage divider (not shown but indicated by terminal T) connected acrossthe anode potential source terminals in the motor generator, thenegative terminal being grounded. Thus a potential drop exists inresistor I 5l which is; sufficient to energize the microphone.

Function (4) of the relay H2 is: to open the circuit between the.negative line terminal -L and all of the receiver gain control circuits,thus silencing the receivers while talking. This circuit when normallyclosed may be traced from relay contacts II2e, -f through relay contactsI I'3fe-e, through conductor I'I8, through branched rheostat. elementsH5, H6 and II "I to certain contacts of the channel selector whichconnect with gain control circuits 43, 44 and 45 leading to the cathodesof R. F. and I. F. amplifier stages (not shown) in the low frequencyreceivers A, B and C. The connections to corresponding cathodes inreceivers D, E and F may also be traced from conductor II'8 throughother contacts of the channel selector and through conductors #0, M and42 to the high frequency receivers. I

Relay II4' when operated as a slave to relay I I2 performs furtherfunctions thus:

(1') Closure of its contacts ab. connects the antenna I23 to conductorH4 which receives output signals from the transmitter I25 by way of oneof the wafers inv a motor-driven gang, switch I26. This switch in its.entirety serves to select. the frequency of the carrier wave. Its, novelfeatures are described. and claimed in my co-pending application Ser.No. 679,343 filed June 26, 1946.,

Function (2). of relay I- I4 is to open the circuit. at its contacts c-bso as to disconnect the antenna from conductor I, 2;'I having branchesto each of the signal input terminals of the six receivers. Duringtalking periods, therefore, no signal can. reach the receivers. Function(3) is carried, out by closure of contacts de, thus grounding the inputcircuits of the receivers: for the purpose. of noise suppression.Function (4); isfulfilled by closure of contacts I I4J'--g andismerelycontributory to the performance (as above described) of function (3) ofrelay II2, that is, to close the microphone circuit. One virtue in thedouble make; and break of this circuit is, to minimize key clicks. The.operation, of; relay H14, is delayed by a, few microsseconds. withrespect. to that of re.- lay II2.

The channel selector switch Although this switch was briefly mentionedin the foregoing description its functions will now be more fullyexplained. Practical considerations, as well as the authorizedassignments of radio frequency channels for Mississippi River shippingservice dictated that the switch wipers be moved to positions 3, 4 or 5for communication on the respective low frequency channels, and thatpositions 1, 2 and 6 be used when communicating on the relatively highfrequency channels.

Position is used for maintaining stand-by conditions in which the outputcircuits of the three low frequency receivers A, B and C are connectedthrough conductor 39, switch wafer 71. and thence through contacts ofthe hook switch II to the loud speaker I I33. Also the output circuitsof the high frequency receivers D, E and F are connected throughconductor 38 and switch wafer i and thence through conductor 31 to theringer amplifier I06.

The gain control circuits for each of the receivers F, E, D, C, B and Ais brought out individually through one of the conductors 40 to 45inclusive and is connected to a wiper On one of the wafers f, e, d, c, band a respectively.

A gang-controlled rheostat comprises adjustable resistors H5, H6 and II!by which the volume of three receivers can be manually set. As shown inFig. 1 resistor H5 at the left hand terminal is connected to differentstationary contacts on wafers 1, c, b, a, e and d. Resistor H6 isconnected to one contact at the 0-position on wafer c and resistor II"!is connected only to the contact at the 0-position on wafer b. The righthand terminals of these three rheostat resistors are connected in commonthrough conductor H3 to movable contact 6 on relay H3, thence throughback contacts 7 of the two relays H3 and H2 and through movable contactII 2e to the L terminal which supplies cathode potential to certainamplifier stages in all of the receivers. Preferably these are the radiofrequency and the first intermediate frequency amplifier stages.

The gain control circuits for the high frequency receivers D, E and Fare connectable directly to conductor H8 when the channel selectorswitch is set to any of the positions 0, 3, 4 or 5. Thus for stand-byconditions and when using any one of the low frequency channels for acommunication the high frequency receivers are all operated at fullgain.

In switch position 1 the gain control circuit for receiver D may betraced through conductor 42, wafer d, resistor H5, conductor H8 andthence through relay contacts to the ,L terminal. Silencing of all theother receivers is then accomplished by opening their gain control circuits. So switch position 1 is useful for communicating on the channelto which receiver D is tuned.

In switch position 2 the gain control circuit for receiver E isconnected through conductor 4|, and wafer e to resistor H5 and iscompleted as described in the preceding paragraph. At the same time allother receivers are silenced. Likewise the gain control circuit forreceiver F is connected through conductor 49 and wafer f to'resistor H5when switch position 6 is selected. All other gain control circuits arelikewise open for that channel selection.

In switch positions 3, 4 and 5 the respective gain control circuits ofreceivers A, B and Care 6. singly connected in each case. to rheostat H5while the gain control circuits of receivers D, E and F are connecteddirectly to conductor H8 and thence to the L supply terminal. Hence, aspreviously mentioned, the high frequency receivers are operated at fullgain and their output circuits are connected to the selective ringer formonitoring purposes during periods when any one of the low frequencychannels is being separately monitored.

Switch wafer g has its stationary contacts I to 6 inclusive connectedindividually to pilot lamps I20 for clearly indicating the setting ofthe channel selector switch when it is moved away from the 0-position.The Wiper on wafer g feeds current to a selected lamp from a 6-voltsource upon closure of contacts dand e when the hand-set I02 is liftedfrom its hook IDI.

Three of the pilot lamps IZII which stand in channel positions 1, 2 and6 respectively are also connected through conductors 35, 34 and 33respectively to contacts in the selective ringer unit I05. Unit I05 isarranged and adapted to close these circuits selectively when it isactuated by the proper sequence of audio frequency call signals; Inpractice the signal pulses are of 600 and 1500 cycle modulation whichare alternated at a rate of 4 to 5 /2 cycles per second. The selectorset on each ship may be arranged to respond to any one of a number offive-digit codes, so that the selective calling of any one of a group ofstations operating on the same carrier frequency is possible. Theterminating pulses of the call signalsignify the communication channelto be used, and by illuminating a particular one of the pilot lamps I20the answering party is enabled to turn his channel selector switch tothe proper position for answering the call on any one of the highfrequency channels.

Switch wafer 7 on the channel selector switch has connections through acable to individual contacts of a motor-driven rotary gang switch IZBatthe main equipment unit. The details of construction and operation ofswitch I26 are not herein given since they are covered in my copendingapplication Ser. No. 679,343 filed June 26, 1946. The setting of switchI26 is accomplished under control of a relay H3 which is in circuit witha selected conductor in cable 5!] and operates to keep the armature ofmotor I28 energized until the setting of switch I26 corresponds withthat of the wiper on wafer 7' of the channel selector switch. The gangswitch I26 performs numerous functions, such as selecting the properradio frequency tuning elements in the transmitting equipment andconnecting the proper output circuit to conductor I24 for feedingoutgoing signals to the antenna I23. The gear train through which themotor I23 drives the gang switch I26 includes preferably a worm.reducing gear I29 and a Geneva movement I30.

In order to listen to a particular receiver the channel selector switchmust be set to the desired channel. This connects the cathodes of theselected receiver to the volume control rheostat I I5 and connects theoutput of this receiver to the loud speaker circuit. When one of thereceivers A, B- or C is selected the high frequency receivers D, E and Fremain connected to the selective ringer, as hereinabove explained. Andwhen one of the high frequency receivers is selected for acommunication, then all'of the non-selected re ce-ivers are silenced byopening their gain control circuits. This arrangement has been found tomeet the practical requirements of two-way radio telephone service inthe Mississippi River and Great Lakes regions.

Transmitter circuits The six sets of pretu-ned transmitter circuits arepreferably of atypewherein carrier power in the '7'5-watt range isgenerated by a crystal controlled tuned anode circuit oscillator. Aseparate quartz crystal and oscillator. anode tank circult is providedfor each transmitting channel. These circuits are switched by wafers onthe gang switch I26.

By means of another wafer on the gang switch I26 the selected, tunedtransmitter unit is connected to a number of parallel-connected poweramplifier stages. Audio frequency output from the modulator unit I 2I isapplied to the screen grids and anodes of those power amplifier stages.The modulate-d output is then coupled to one of six sets of antennatuning circuits connections being made through still another wafer ofthe motor-driven gang switch. Finally, the antenna conductor I247 isconnected to the selected antenna tuning circuit, through one more waferof the gang switch in unit I26. All these details of transmitter circuitswitching may readily be worked out for different transmitter circuitdesigns by those skilled in the art. For purposes of this: disclosure,therefore, it is preferred to symbolize by block diagram the transmittercircuits I25 and the gang switch l'26 for channel frequency selection.It will be understood, however, that for the practical operation of myinvention it is essential that the motor-driven gang switch- I2'6 becapable of automatic adjustment to any position corresponding topositions 1 to 6 inclusive in the manually operable channel selectorswitch at the control unit. Furthermore, since the motor-driven switchI26 is capable of rotation in one direction from any previous settingto. any desired new setting, it matters not where it is set at the timeof shutting down the transmitter and of turning the manually operableswitch to the stand-by position. In fact, the motor-driven gang switchhas no stand-by position, for it needs none. But itv always assumes aposition corresponding to positions 1 to 6 inclusive of the manuallyoperable gang, switch, the latter exercising its control through itswafer 7'.

The earphone, microphone, modulator and pushbutton The cord I3I for thehand set H32 contains separate conductors for the microphone, theearphone and. the push-button III. Also for these three elements thereis a common return conductor connected to ground.

When using the earphone the output from one of the receivers is broughtthrough one or the other of the conductors 38-39 to the wiper on channelselector switch Wafer h and thence through conductor I32, through closedcontacts I) and a of hook switch IIH, and manual switch IIEl, this lastbeing thrown to make connection with the earphone. The return circuit isthrough ground to a grounded terminal of the secondary winding (notshown) on the receiver output transformer. While listening the antennaI23 is connected through normally closed contacts b and o of relay I I4to all of the receiver input terminals in parallel.

The microphone is connected. through a circuit which may be traced fromground through the microphone, thence through the modulator unit I2I,and through a 5. ohm resistor I51 to ground. By closing contacts f and gof b and a of relay II2v a. suitable voltage drop is produced throughresistor I5! which constitutes the D. C. supply to the microphone, asheretofore indicated.

The push-button I I I- is connected through conductor 30. to the windingof relay I I2 and thence to the C terminal of the transmitter powersupply. The +C terminal is grounded. The transfer functions of relays H2and IM as controlled by the push button I I I have already beendescribed. It should here be noted, however, that the receivers can allbe silenced in two Ways-one by operation of the push-button-controlledrelay II2 which opens its contacts e and f; the other by operation ofrelay I I3 which opens its contacts e and ,f. In the latter case thereceivers are silenced during the movement of the channel selectorswitch I26 from one to another position. These four relay contacts justmentioned when normally closed complete the receiver gain controlcircuits to the L power supply terminaL, as hereinabove set forth.

The hoolc switch When the hand-set I02 is lifted from, its hook IllIcontacts of the latter operate as follows: Contacts b and 0 open tosilence the loud speaker. If loud speaker operation is preferred toearphone reception while engaged in a conversation, then switch H0 maybe thrown to the proper position for that purpose. Closure ofswitch-hook contacts a and b connects the receiver output to the movablecontact on switch I-IIl.

Closure of switch-hook contacts at and e supplies potential froma+6-volt source terminal to the wiper on channel selector switch wafer 9so as to light up one of the channel indicating pilot lamps I220. Thenegative terminal of this 6-volt source is the same as the -L terminal.So the return circuit common to all the lamps I20 joins that of the bellI64 and includes conductor -32, contact ,1 on relay 602 which isdirectly connected to the -L terminal.

Closure of switch-hook contacts 1 and g connects conductors 9 and 36 toconductor 46, whereby +L potential is supplied (1) through switch water9' and conductor 50 to relay II 3 for operating the motor-driven channelselector switch I26; (2) through conductor 46 to terminal 209 on thestarter coil of the motor-generator; and (3) through conductor 46 to theWinding of a so-called lock-out relay 604- in the junction box. Thefunction of this relay will presently be explained. The three branchcircuits closed by switch-hook contacts f and g. are all returned to.the L line terminal.

The junction boa:

The junction box contains terminal boards for the inter-connectingcables which are necessary for remote control of the. radio equipmentfrom either of two remote control stations. The junction box alsocontains the necessary relays B01, 602 and 604 for switchingthe controlcircuits from one remote control unit to the other.

As shown in Figure 2 the relays EDI and 602 have their windingsconnected in parallel and each relay operates nine movable contacts mostof which engage with both front and back stationary contacts.Practically it is preferred to use three relays in place of relays GUI:and 602 in order that the spring load of each relay coil may not beexcessive. The assignment of contact springs to the different circuitsis immaterial aside from the fact that the front contacts, with oneexception, must all lead to components in the control unit A shown inFigure 1 and the back contacts lead to corresponding components in thecontrol unit B. To avoid unnecessary tracing of circuits the connectionsbetween the back contacts and control unit B have not been shown.

Normally control unit B is maintained in control of the system, relaysEM, 602 and 603 being unenergized. Control may be switched to controlunit A by momentarily closing switch I09A on that unit. This energizesrelays 60I and 602, the circuit for which may be traced from the +Lterminal at switch I01 in station A through one of the conductors 80 orBI, switch I01 at station B, conductor 9, switch I09A (momentarilyclosed), conductor 48, contacts and b of relay 604, conductor 80 andthrough the coils of relays SM and 602 to the L terminal.

The relay circuit just traced is locked up by closure of contact e andits front contact on relay 602, this locking circuit extendingtemporarily (until the hand-set I02 is lifted from its hook) from liveconductor 9 to conductor I9, thence through contacts of switch I09B, andconductor 80 to the coils of relays SM and 602.

Now the exclusive use of control unit A for the period of a telephoneconversation may be insured by lifting the hand-set thereat. Thisenergizes the lock-out relay 604 in the following manner: Live conductor9 connects through contact d of relay 602 to conductor 36, thencethrough contacts g and f of switch hook IOI, conductor 46, contact 0 ofrelay 602 and the coil of relay 604 to the L terminal. This circuit isalso branched to the starter terminal 209 so that the motor generatormay be started up for supplying power to the transmitter.

The lock-out function of relay 604 is eifected this way: Closure of itscontacts e and d makes direct connection between the +L terminal andconductor 9, and since relays 602 and 604 are both energized the +Lpotential traverses contacte of relay 602, conductor 19, contacts a andb of relay 604 and conductor 80 to the coils of relays GM and 602. Notethat contacts a and b of relay 604 are in shunt with switch I09B incontrol unit B, so that the opening of that switch cannot result in lossof control at the control unit A so long as its hook-switch is up.Furthermore, the switches I01 are effectively shunted by contacts d ande on relay 604, thus preventing the power from being shut off at theunused control unit.

When control unit B is to be used, the operator will first see that thepower switch I01 iscorrectly set for lighting the Power on pilot lampI08. If no sound is heard in his speaker he operates switch I09Bmomentarily in order to break the locking circuit that held relays SMand 602 energized by previous use of control unit A. Control. is thenreturned to control unit B, provided the operator at control unit A hashung Now the lifting of the hand-set at control unit B results inenergizing the look-out relay 604 through circuits which are like thosepreviously described in reference to control unit A, but which traversethe back contacts associated with movable contacts d and c on relay 602.Note that contact 0 of relay 604 is connected through conductor48 to acontact of switch 109A at control 10 unit A. Therefore, the opening ofcontacts b and con relay 604 establishes exclusive control at'controlunit B. Again, while relay 604 is energized the power switches-I0? atthe two control units are shorted by closure of contacts d and e onrelay 604. So the two switches I07 and I09A at control unit A are bothdisabled during a tele-' phone conversation carried on at control unitB.

Complete privacy of use of either control unit is insured by means ofthe transfer switch contacts of relays GM and 602. Thus, consideringrelay 60! when it is not energized, the receiver output circuits 38and'39 are carried to the manually operated channel selector switch 220at control unit B. So, also with'respect to the gain control circuits 40to 45 inclusive. And conductor 31 which leads to the input terminal ofthe ringer amplifier is broughtback from control unit B through the backcontact nearest the core of relay 60L" r Considering relay 602 when itis not energized, its back contacts which are associated with movablecontacts a and dare connected to the microphone and push-buttonrespectively on the hand-set I02B at control unit'B. Back contactsassociated with movable contacts 17, c, and I lead exclusively to thehook switch and bell (not shown) at control unit 'B. Also the pilotlamps for channels I, 2 and 6 at the control unit B are connected to theselective ringer I05 only when movable contacts g, h and i on relay 602rest against their associated back contacts.

All of the conditions set forth in the two preceding paragraphs aremodified by the energization of relays 60I and 602 so that completeprivacy is obtained at control unit A whenever desired.

Operation In the preferred embodiment of my invention the operatingprocedure for monitoring and answering calls is as follows:

(1) Turn the power switch I01 so that the pilot lamp I08 glows.

(2) Allow 15 seconds for receiver tubes to warm (3) .Turn the channelselector switch to Stand-by, the (l-position. Adjust the receiver volumecontrol clockwise as far as possible. Atmosphere noise and incomingcalls on channels 3, 4 and 5 will be heard from the loud speaker.Incoming calls on channels I, 2 and 6 will actuate the automatic ringerI05. When the bell I04 rings the incoming call will cause one of thepilot lights I20 to be illuminated corresponding to the channel numberto be used in answering the call.

(4) If no sound isheard from the loud speaker, operate the control unitselector switch .I09A or I09B momentarily and release. This shiftsreception to the adjacent speaker.

(5) When the channel selector switch is on channel 3, 4 or Efincomingcalls on channels I, 2 and "6 will still actuate the selective ringer.Listening on channels I, 2 or 6 will disable the selective ringer.

(6) Remove the hand-set I02 from its hook and thereby cause themotor-generator to be started up. The motor-generator comes up to fullspeed in approximately three seconds. The warming-up period for thetransmitter tubes is scarcely more than this, so that, for practicalpurposes the transmitter is ready to go on the air as soon as one haslistened for a reasonable time to make sure of a clear channel.

11 Closure ofswitch-hook contacts i and g causes a restoring voltage to:be applied to the stepping magnet (not shown) in the code selector,whereby the code wheel is restored to normal and the ringing of the bell404 ceases.

(7) If it is desired to listen on a single channel to the exclusion ofall others, the channel selector should be turned to the desired channelnumber and the'volume control adjusted to a satisfactory level eitherfor loud speaker use or ear-phone use.

The calling procedure is relatively simple:

(1) Turn the channel selector switch to the desired channel number andlisten for one minute to make sure that the channel is not in use.

(2) Set the switch H to the desired position for use of either the loudspeaker or the earphone.

(3) Remove the hand-set H12 from the hook I DI and wait for the channelpilot lamp to light up.

(4) To talk, hold down the push-button- Ill. Release to listen to theother party.

It is, of course, important to replace the hand set on the hook aftercompleting a call. The channel selector switch should also be turned tostand-by (0) position and the receiver volume adjusted to a sufficientlyhigh level so that the next incoming call will be clearly heard on theloud speaker.

For service in the Mississippi River region the radio frequency channelsatpresent assigned and their uses are as follows:

connect a gain control circuit to the corresponding amplifier stage ofthe selected receiving unit through said volume regulator, (2) toconnect the same selected receiving unit to said audible responsivedevice, and (3) to disconnect the gain control circuits from theremainingreceiving units, thereby to silence the same.

2. In a selective switching arrangement for a radio-telephoninstallation, a multiple-position gang switch the wipers of which have astand-by position and to any position corresponding to a selectedcommunication channel, and, connected thereto, a plurality of receivingunits each differently tuned to one of the channel frequencies to beused, a selective ringer responsive to code signals when received oncertain of said channels, an audible responsive device, a volumeregulator and gain control circuits individual to certain amplifierstages in each of said receiving units, said gang switch being operablein a stand-by position: (1) to connect a number of said gain controlcircuits through said volume regulator to the corresponding amplifierstages, (2) to connect the corresponding receiving units to said audibleresponsive device, and '(3) to connect the remaining Frequency 2206 2738To communicate with New Orleans only. Ship to Ship Various ShoreStations.

Short Distance-Day-time Coverage Long Distance-Night Long Distance Day &Night Day-time only The frequency assignments as given in the abovetable are those now authorized for transmitting from Mississippi Riverships. Reception is at the same frequencies except on channel 3, sinceNew Orleans transmits at a frequency of 2598 kc.

For the Great Lakes region and for other radiomarine services thefrequency allocations would be difierent, of course, so that nolimitations are to be imposed upon the uses of my invention fortransmission and reception of radio communications at any frequencieswhatsoever.

It will be understood by those skilled in the art that variousmodifications of my invention may be made without departing from itspatentable scope.

I claim:

1. In a selective switching arrangement for a radio-telephoneinstallation, a multiple-position gang switch the wipers of which haveselected positions each corresponding to a selected communicationchannel, a plurality of receiving units each having one amplifier stageand each differently tuned to one of the channel frequencies to be used,an audible responsive device, volume regulators, and gain controlcircuits one of each corresponding to one amplifier stage in each ofsaid receiving units, said gang switch being 'connected to saidamplifier stages, said response device, and said volume regulators andgain control circuits, said gang switch being operable: (l) to thechannel frequencies to be used, a selective ringer responsive to codesignals when received on certain of said channels, an audible responsivedevice, a volume regulator and gain control circuits individual tocertain amplifier stages in each of said receiving units, said gangswitch being operable in certain of its channel selecting positions: (1)to connect the gain control circuit to the selected receiving unitthrough said volume regulator; (2) to connect the same receiving unit tosaid audible responsive device; (3) to disconnect the gain controlcircuits of certain others of said receiving units, thereby to silencethe same; and (4) to connect the remaining receiving units at full gainto "said selective ringer.

4. In a selective switching arrangement for a radio-telephoneinstallation, a multiple position gang switch the wipers of which havedifferent selective positions corresponding to selected radio frequencychannels, including "certain channels in a high frequency band and otherchannels in a low frequency band, an audible responsive device, aselective ringer, a plurality of receivers, adjustable gain controlcircuits each corresponding to certain amplifier stages in each of saidplurality of receivers, said receivers being individually tuned todifferent ones of saiclchannels and thereby including low frequency andhigh frequency receivers each having output terminals and circuit meansconnected to the wipers and stationary contacts of said gang switch andalso connected to: (a) said responsive device, (In) said ringer, (G) theadjustable portions of said gain control circuit arrangement, and (d)the output terminals of said receivers, said means being operable inaccordance with the setting of said switch wipers: (1) to connect theoutput terminals of said low frequency receivers to said audibleresponsive device, (2) to connect the gain control circuit to theselected receiver, (3) to disconnect thegain control circuits from theremaining low frequency receivers, and (4) to connect the outputterminals of said high frequency receivers to said selective ringerwhile maintaining the corresponding gain control circuits operable atfull gain.

5. Ina selective switching arrangement for a radio-telephoneinstallation, a multiple position gang switch the wipers of which havedifferent selective positions corresponding to selected radio frequencychannels including certain channels in a high frequency band and otherchannels in a band of relatively low frequency, an audible responsivedevice, a selective ringer, adjustable gain control circuits individualto certain amplifier stages in each of a plurality of receivers, saidreceivers being individually tuned to different ones of said channelsand thereby including low frequency and high frequency receivers eachhaving output terminals, and circuit means connected to A the wipers andstationary contacts of said gang switch and also connected to saidresponsive device, said ringer, the adjustable portions of said gaincontrol circuits, and the output terminals of said receivers, said meansbeing operable in accordance with the setting of the switch wipers:

(1) to connect the output terminals of said high frequency receivers tosaid audible responsive device, (2) to connect the gain control circuitto the corresponding selected amplifier stage, and v(3) to disconnectthe gain control circuits from the remaining receivers, thereby tosilence the same during atelephone conversation.

6. In a selective switching arrangement for a radio-telephoneinstallation, a multiple position gang switch the wipers of which haveselectively difierent positions corresponding to selected radiofrequency channels including certain channels in a high frequency bandand other channels in a band of relatively low frequency, and, connectedto said switch, an audible responsive device, a selective ringer,adjustable gain control circuits individual to certain amplifier stagesin each of a plurality of receivers, said receivers being individuallytuned to diiferent ones of said channels and thereby including lowfrequency and high frequency receivers each having output terminals, andcircuit means connected to the wipers and stationary contacts of saidgang switch and also connected to said responsive device, said ringer,the adjustable portions of said gain control circuits, and the outputterminals nel selectorswitch for usein a radio telephone system, saidswitch comprising a plurality of contact wafers each having a movablecontact wiper and an. associated array of stationary contacts, allwipers being gang-controlled, and, connected to said switch, a pluralityof receivers each tuned to adifferent carrier frequency and each havingan output circuit and a gain control circuit, a manually operable volumeregulator of the rheo stat type, a listening device and a selectiveringer unit, said switch being'operable under stand-by conditions (1) toconnect the output circuits of certain receivers to said listeningdevice and simultaneously connect the corresponding gain controlcircuits to its receiver through said volume regulator, and (2) tosimultaneously connect the output circuits of the remaining reif-saidreceivers, said means being operable in ceivers to said selective ringerunit, with the gain control circuits for these remaining receivers beingshunted across said volume regulator, and said switch having otherpositions inwhich the output circuit of a selected receiver isconnected. to said listening device and the corresponding gain controlcircuit is connected to the selected each comprising a hand-set, achannel selector switch to selectively choose one of said circuits whenconnected to said transmitter receiver, and remote-control switchingmeans, and a junction box containing relays connected to and subject tocontrol from said remote control units, said remote control switchingmeans being connected to said circuits,- said hand-set, and said channelselector switch and operable: (1) to connect the channel selector switchat a particular one of said control units to said transmitter receiver,and (2) to actuate at least two of the relays in 7 said junction box,thereby to cause the other control unit to be disconnected from thereceiver.

10. In a radio telephone system, a transmitterreceiver installationcomprising pre-tuned radio frequency circuits for selective use on aplurality of different channels, a motor-generator for energizing thecircuits of the transmitter, a direct current source for energizing thereceiver circuits and for driving said motor-generator, two remotecontrol units each comprising a hand-set, a channel selector switch andremote control switching means, and a junction box containing relayssubject to control from one of said control units whereat controlis'preempted, said remote control'switching means being operable: 1) tocoin nect the direct current source to said generator and to-connectsaid direct current source to said receiver circuits, (2) to connectsaid pre-tuned circuits to the channel selector switch at the premptingcontrol unit, and (3) to actuate at least two of the relays in saidjunction box, thereby to cause the unused control unit to bedisconnected frequency channels in one housing and two control unitsremotely situated with respect toeach other and to said housing, audibleresponsive means at each of said control units and connected selectivelyone at a time to said receiving apparatus, a gang switch at each controlunit and constituting means at times operable for selecting a desiredradio frequency channel of two-way communication for use a saidtransmitting and receiving apparatus, control unit disabling means, andrelay means operable under control of switching devices at a preemptingcontrol unit to connect said disabling means to the other control unitthereby locking out and disabling the other control unit to prevent thesame from exercising control and interfering with a telephonevconversation which is commenced at said preempting control unit.

12. A system according to claim 11 and including means under control ofsaid gang switch and operable by setting the same to a stand-by positionto connect a plurality of said radio frequency channels to saidreceiving apparatus whereby a certain plurality of radio frequencychannels are simultaneously monitored by said receiving apparatus and toconnect the receiving apparatus to the audible responsive means wherebythe audible responsive means receives the receiving apparatus output andis audibly responsive thereto.

13. A radio telephone system comprising a remote control unit andtransmitting and receiving apparatus including components thereof whichare pre-tuned for operation on different radio frequency channels, saidapparatus bein separately housed with respect to said remote controlunit, a manually operable gang switch in said control unit, said switchhaving a standby position connecting aplurality of componentssimultaneously in circuit in said receiving apparatus for elfectingmultiple channel monitoring of incoming signals by said receivingapparatus, and having single channel selecting positions connectingselected components in circuit in said apparatus for obtaining singlechannel operation of the transmitting and receiving apparatus, amotor-driven gang switch in the housing of said transmitting andreceiving apparatus, electrical means for causing the motor-driven gangswitch to assume any one of a plurality of single channel positionscorresponding to that to which the manually operable gang switch isconcurrently set, said motor-driven gang switch constituting meansconnecting a single selected component in circuit in said transmittingapparatus for causing said transmitting apparatus to be tuned to adesired channel frequency corresponding to the selected receiverfrequency, means connected to the manual gang switch and operable byselectively setting the manual gang switch, to a single channel positionfor conditioning the receiving apparatus to translate incoming signalsonly as received on said desired channel frequency, and means controlledby the two gang switches for suppressing the operation of transmittingand receiving components which are tuned to non-selected channelfrequencies.

14. A system in accordance with claim 13 and including an additionalremote control unit similar to the first remote control unit andselective means for obtaining exclusive use of either of the two remotecontrol units while looking out control of the transmitting andreceiving apparatus by the non-selected remote control unit.

15. A radio telephone system comprising a re- 16.. mote control unit andreceiving apparatus including components thereof which are pre-tuned foroperation on different radio frequency channels, said apparatus beingseparately housed with respect to said remote control unit, a manuallyoperable gang switch in said control unit, said switch havin a stand-byposition to connect a plurality of components in said apparatus forefiecting multiple channel monitoring of incoming signals by saidreceiving apparatus, and having other positions to connect a selectedcomponent in said apparatus to provide reception on a selected radiofrequency channel, output circuits and gain control circuits for each ofsaid differcntly tuned receiving apparatus components, said output andgain control circuits having connections completed by said manuallyoperable gang switch in selected positions thereof whereby saidapparatus effectively receives single channel voice reception and theconcurrent reception of incoming selective code signals by others ofsaid receiving apparatus components.

16. A radio telephone system comprising transmitting and receivingapparatus arranged for two-way service on any one of a plurality ofradio frequency channels and having means for monitoring simultaneouslya plurality of channels for incoming signals, a pair of remote controlunits each including a microphone-earphone hand-set, and controlswitches for establishing different circuit conditions in said system, apush-button on each hand-set, relay means subject to control by saidpush-button for conditionin said transmitting apparatus to radiate asignal modulated by a microphone of a selected hand-set, said relaymeans being at the same time effective for silencing the receivingapparatus, other relay means automatically operable to disconnect theother control unit until the hand-set which is in service is hung up,and channel selecting means operable at times to condition thetransmitting and receiving apparatus for single channel twowaycommunication and at other times for multiple channel monitoring ofincoming signals.

17. A system according to claim 16 and including a selective ringer anda loud speaker, circuits to connect certain channel-tuned units of saidreceiving apparatus and said loud speaker, other circuits to connect theringer with the remaining units of said receiving apparatus; saidchannel selecting means being effective to make all of said circuitconnections, and means for controlling the volume of response in. theloud speaker.

GEORGE G. BRADLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,064,905 Green Dec. 22, 19362,093,847 Pruden Sept. 21, 1937 2,137,023 Monk Nov. 15, 1938 2,164,960Stockton et al.- July 4, 1939 2,176,868 Boswau Oct. 24, 1939 2,265,056Bowers Dec. 2, 1941 2,399,738 Howe May 7, 1946 2,419,593 Robinson Apr.29, 1947 FOREIGN PATENTS Number Country Date 311,450 Great Britain May13, 1929

